The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Vehicles include an internal combustion engine that generates drive torque. More specifically, an intake valve is selectively opened to draw air into a cylinder of the engine. The air mixes with fuel to form an air/fuel mixture that is combusted within the cylinder. The air/fuel mixture is compressed and combusted to drive a piston within the cylinder. An exhaust valve selectively opens to allow the exhaust gas resulting from combustion to exit the cylinder.
A rotating camshaft regulates the opening and closing of the intake and/or exhaust valves. The camshaft includes cam lobes that are fixed to and rotate with the camshaft. The geometric profile of a cam lobe determines a valve lift schedule. More specifically, the geometric profile of a cam lobe generally controls the period that the valve is open (duration) and the magnitude or degree to which the valve opens (lift).
Variable valve actuation (VVA), also called variable valve lift (VVL) improves fuel economy, engine efficiency, and/or performance by modifying valve lift and duration as a function of engine operating conditions. Two-step VVA systems include VVL mechanisms, such as hydraulically-controlled, switchable roller finger followers (SRFFs). A SRFF associated with a valve (e.g., the intake or exhaust valves) allows the valve to be lifted in two discrete modes: a low lift mode and a high lift mode. Generally, the valve lift associated with the high lift mode is greater than the valve lift associated with the low lift mode.